V LBI E xtragalactic Co mpact R adio S ource S urvey Lee, Sang-Sung

1. VLBI Extragalactic Compact Radio Source Survey Lee, Sang-Sung 2009EastAsiaVLBIWorkshop

2. Collaboration • Initiated by collaboration btw VERA and KVN • VERA • Mareki Honma • KVN • Bong Won Sohn • S. Lee • Accelerated by motivation from • Yuri Y. Kovalev (MPIfR) • Leonid Petrov (GSFC/NASA)

3. Contents • Introduction • Project: VECoRSS • Goals • Motivations • Substance • Plan

4. Active Galactic Nuclei (AGN) Observables: Flux density (S)Angular Size (θFWHM)Apparent jet speed (βapp) Brightness Temperature Tb Marscher 2005

5. Brightness Temperature Brightness temperature: A temperature that a source should have as if it was a black body to radiate a specific intensity *Gaussian pattern of brightness distribution* Source rest frame Inverse Compton limit: Whenever Tb > 1012 K, inverse Compton scattering of radio photons dominates, and most of the energy will be radiated in X-ray. (Kellermann & Pauliny-Toth 1969) Equipartition limit: Sources radiate at Tb ~ 5 x 1010 K when energy densities in relativistic particles and magnetic fields are in equipartition. (Readhead 1994) High-resolution VLBI surveysenable to statistically study the brightness temperatures of compact radio sources and to test the theoretical models of relativistic outflows (e.g., Marscher 1995).

6. Relativistic effects and lower limit Relativistic effects: Radiation emitted from a jet component moving at a velocity of with an angle to the line of sight can be Doppler boosted. Doppler factor Apparent jet speed Lower limit of Tb: Minimum resolvable size dmin a,b: axes of restoring beamSNR: signal-to-noise ratio : weighting function When d < dmin, the lower limit of Tb should be estimated with d = dmin.

7. VLBI Core and its opacity effect • VLBI core is located at a region where in the jet. • Under the equipartition condition, the absolute position of the VLBI core r is related to the total radiated synchrotron luminosity Lsyn Lobanov (1996) In order to investigate the physics of compact radio jets in sub-parsec scale regions, we need to observe them at higher frequencies with high resolution (high resolution VLBI survey).

8. Project: VECoRSS VECoRSS: VLBI Extragalactic Compact Radio Source Survey FS43: Fringe Survey at 43GHz pFS43: pilot Fringe Survey at 43GHz VIS43: VLBI Imaging Survey at 43GHz

9. PC-scale structureof compact radio sources VECoRSS: Goals KVN ICRF International collaboration NASA GSFC MPIfR Calibrator43GHz VERA TrainingVLBI experts

10. Large VLBI surveys *sub-sample. **VERA 22 GHz survey is done in collaboration with H. Kobayashi, T. Jike, M. Honma, K.M. Shibata, T. Hirota.

11. VECoRSS: Motivation • Only a few 100 sources have been observed/imaged at 43 GHz for geodetic/astrometric purpose (VLBA, Lanyi et al). • A KVN/VERA fringe survey at 43 GHz should be considered for VERA, KVN, VSOP-2, etc. • VERA: needs a full list of extragalactic calibrators at 22/43 GHz for dual-beam Galactic astrometry. (e.g., VERA fringe survey at 22 GHz; Petrov et al 2007, Full sky VERA fringe survey at 22GHz ongoing; Petrov et al.) • KVN: needs the list of calibrators at 22/43 GHz for multi-freq. phase-referencing observation at 22/43/86/129 GHz. • VSOP-2: needs preparatory surveys for identifying suitable radio sources for phase referencing observation at 8/22/43 GHz (VSOP-2 pre-launch survey at 43 GHz). • A follow-up VLBI imaging survey at 43 GHz with a complete sample of compact radio sources is required to study compact AGN jets.

12. pFS43: pilot Fringe Survey at 43 GHz • pFS43 (2009) : A 24-hr pilot observation of ~ 270 compact radio sources out of 550 candidates selected (with VERA+KVNYS). • Goals: to answer the following questions; • What is the baseline sensitivity of VERA (+KVN) at 43 GHz : ∆SVERA. Expected value ∆SVERA ~ 150 mJy (VERA team, priv. comm.) • How to schedule the fringe survey? • How to fringe-fit? • What are the criteria for selecting the candidate sources? • What are the amplitude calibrators? • How often the amplitude calibrators should be observed? • What will be the accuracy of amplitude calibration? • What is maximal integration time?

13. pFS43 - proposal • Source selection criteria: 270 out of 550 candidates • Correlated flux density of Sc ≥ 300 mJy on baselines of 170 ~ 250 Mλ at 8 GHz based on the catalogs of VCS1-6 and ICRF • Compactness of Sc/SVLBA ≥ 0.4 at 8 GHz • Detected sources in 3mm VLBI survey (Lee et al. 2008) • Correlated flux density of S22 ≥ 500 mJy on baselines of 100 ~ 200 Mλ at 22 GHz base on the VERA Fringe survey at 22 GHz (Petrov et al. 2007) • Amplitude calibration: • Amplitude calibrator : 20 sources from the Blazar (2-3 months) monitoring program at 43GHz (Marscher et al. Boston Univ.) • Observation: • Six 4-hour observations with dynamic scheduling • Each source will be observed for one/two scan(s) of 2-min duration. • Amplitude calibrator should be observed every 20 min.

14. Selected sources • 270 objects selected for the pilot observations • Group1 (90) : Sc > 500 mJy, Sc/SVLBA≥ 0.4 • Group2 (133) : 500 mJy ≥ Sc ≥ 300 mJy, Sc/SVLBA ≥ 0.4 • Group3 (47) : Sc < 300 mJy, Sc/SVLBA ≥ 0.4

15. Sky distribution

16. Observed sources at 1st epoch Preliminary detection rate 40% with FRING(AIPS) 70% with VEDA

17. Observed sources at 1st and 2nd epochs

18. FS43: Fringe Survey at 43 GHz • FS43 (2010-2011) : Survey observations with EAVN-Array43 (VERA, KVN, Nobeyama, Kashima) • Sources with expected Sc > ∆SVERA • Each source observed for one or two scans. • The first whole-sky fringe survey at 43 GHz in Northern hemisphere. • Spectral index (at 22-43GHz) obtained from KVN data.

19. East Asian VLBI Network (EAVN) • EAVN-Array-Q (so called) : • KVN(3x21m) + VERA(4x20m) + Kashima(34m) + Nobeyama (45m) EAVN-Array43 0.7 mas@43GHz

20. VIS43: VLBI Imaging Survey at 43 GHz • VIS43 (2012-2013) : A follow-up VLBI imaging survey with a complete sample (EAVN-Array-Q + VLBA) • A complete sample based on the results of FS43 • Improve the data base of AGN VLBI images at 43 GHz • A good database for International Celestial Ref. Frame (ICRF-ext2) • Statistical study of intrinsic properties of relativistic jets. • Resolution of the global VLBI survey at 43 GHz will be matched with that of VSOP-2 at 22 GHz • Comparison of structural information and morphology at matched resolution • Comparison of Tb distribution at 22/43 GHz • To see if there is any difference. • To see if the difference is coming from jet stratification or opacity effect.

21. Statistical study of compact jets • Change of Tb in a jet => acceleration/deceleration of relativistic jets A VLBI imaging survey at 43 GHz is required to fill this gap to confirm the possible trend of Tb Change of Tb Tb increases up to 20 GHz and then starts to decrease At 86 GHz, Tb are systematically low.

22. Change of Tb in a jet

23. (Vlahakis & Koenigl (2004) r [pc] Change of Tb in a jet Compact jets may be accelerated by magnetohydrodynamic (MHD) forces.

24. VECoRSS: Plan A complete sample of calibrators ICRF-ext2 pFS43 VSOP-2 2009 2010 FS43 2011 FS43 VERA 2012 2013 VIS43 VIS43

25. Thank you!